FEMA's coastal flood studies and coastal flood hazard mapping, like all other hazard studies and maps, are not perfect. Some uncertainty will always be associated with Special Flood Hazard Area (SFHA) limits and Base (1-%-annual-chance) Flood Elevations (BFEs). Through our modeling procedures, FEMA strives to reduce the uncertainty and to calculate the average of the likely range of BFEs.
In other words, the elevations and lines shown on the FIRMs are just as likely to under-predict the true 1-%-annual-chance flood conditions as they are to over-predict them.
Please note that flood risk exists even for structures located outside the SFHA. Past floods have exceeded the 1-%-annual-chance flood and future floods may as well. About one in five NFIP claims come from property owners whose structures are located outside the mapped SFHA.